I use cinder blocks to hold the ends of the poles, you can lay them on their side, stand them up, or put the ends of the poles in holes for a variety of heights. If you use them standing up with poles across the top you can use little shims to keep the poles from rolling. The entire thing will topple over if it gets knocked to hard though. I also like PVC poles they are light and easy to move around and store. The only draw back is they are easily knocked over. The cinder blocks also stack easily in a corner. I have also used barrels of varying sizes, logs, larger tree limbs and tires. Be creative, I drive around on garbage day looking for things to add to my obstacle course, my neighbors think I am nuts.